Fabrication of semiconductor devices is a multi-step process of forming features on a semiconductor substrate (wafer) or other substrate. Steps can include material growth, patterning, doping, deposition, etching, metallization, planarization, and so forth. Features formed on a substrate can include various transistors. Transistors can be planar or non-planar, and can also have single gates or multiple gates.
Various etching processes benefit by being able to etch one material relative to another material so that one material is removed, while another material largely remains on the substrate. For example, photoresist has its name in part because it resists being etched by dry plasma etch processes. Photoresist materials are conventionally formed into relief patterns which function as etch masks to etch transfer a pattern into one or more underlying materials.